One known process for producing bio-oil from biomass includes a method called fast pyrolysis. Fast pyrolysis includes heating the biomass at elevated temperatures—e.g., 400 to 550° C.—in the absence of oxygen or in low-oxygen environments. Bio-oil may also be produced by slow pyrolysis, liquefaction or other alternative method. Any biological material or coal can be pyrolyzed, liquefied, or treated by an alternative technology to produce bio-oil.
Regardless of the method utilized for its production, bio-oils share some similar characteristics. More specifically, bio-oil is a dark brown colored liquid with pungent phenolic odor; bio-oil chemical properties vary with material utilized for its production or the conditions under which it is produced. Untreated bio-oil can be used as a boiler fuel. It has environmental advantages when compared to fossil fuels because, when burned, bio-oil produces less pollution than fossil fuels, specifically, half the NOx, negligible quantities SOx emissions (which contribute to acid rain), and it is CO2 neutral.
However, there are still some disadvantages with using untreated bio-oils. For example, untreated bio-oil has significant water content, high acidity, immiscibility with petroleum products, viscosity increase over time, and a distinctive odor. In addition, when tested for use as an engine fuel, bio-oil caused engine damage in many types of engines. In light of the many disadvantages of using untreated bio-oil as a fuel, it has not been adopted for widespread commercial use.
Presently, bio-oil upgrading techniques include hydrodeoxygenation, catalytic pyrolysis, and steam reforming mainly to reduce the oxygen content present in the bio-oil. Hydrodeoxygenation and catalytic pyrolysis techniques require extensive capital cost, complicated equipment, and a high amount of hydrogen consumption. Hydrodeoxygenation has been limited by rapid catalyst coking and reactor clogging. It is well known that theoretical hydrocarbon yields from biomass or coal derived bio-oil are relatively low.
It is clear that there is a need to develop new bio-oil conversion technologies that are more cost effective, increase fuel yields, and produce more fungible fuels. To this end, embodiments of this invention include a bio-oil pretreatment procedure to increase the bio-oil carboxylic acid content. By this method, two pretreatment steps, 1) oxidation and 2) acid anhydride treatments, may be performed depending on the conversion method and fuel type desired. The oxidation or acid anhydride steps may be performed singly or both may be applied in any order. The oxidation step converts some functional groups contained in the bio-oil to their corresponding carboxylic acid derivatives. An aspect of the invention is the conversion of the aldehyde and ketone functional groups to carboxylic acids. It is the aldehyde and ketone functional groups that are responsible for much of the coking experienced during bio-oil deoxygenation.
The acid anhydride treatment converts bound-water present in the bio-oil or oxidized product to carboxylic acids. The product produced from the combined oxidative and acid anhydride treatment is termed hyper-acidified product in this application.
The oxidation pretreatment to increase carboxylic acids in the raw bio-oil provides a route to an oxidized product that may produce more than a single biofuel. The oxidized bio-oil has an acid value of 130 to 165 mg KOH/g (the acid value may be more or less than the 130 to 165 range depending on the oxidation method applied and its severity). This is much higher than the raw bio-oil acid value that may range from 85 to 95 mg KOH/g. The composition of the oxidized product also varies from raw bio-oil depending on the nature of the pretreatment.
The oxidized product may be utilized to produce three boiler fuel types and three fully deoxidized hydrocarbon mixtures. The first boiler fuel type may be produced by catalytic partial deoxygenation of the original oxidized product. An aspect of the invention is that presence of a high proportion of carboxylic acids allows the utilization of syngas as a deoxygenation gas. Without the high acidity of the oxidation and acid anhydride treatments the bio-oil turns to sludge in the presence of pressurized syngas. Thus, only the acid pretreatment allow syngas, with a low hydrogen content, to be utilized to reduce the amount of hydrogen consumed during deoxygenation.
The partial deoxygenations referenced in this application may be achieved in the presence of pressurized syngas or pressurized hydrogen. For application of pressurized hydrogen, the catalyst will be a suitable partial deoxygenation catalyst. For application of pressurized syngas the catalyst must be a suitable partial deoxygenation and water gas shift catalyst (WGS). The catalyst may be bi-functional for partial deoxygenation and WGS or may be a mixture of a deoxygenation and WGS catalyst. The second fuel type requires esterification with addition of alcohol. Again, partial deoxygenation and WGS may be performed in the presence of a suitable catalyst or mixture of catalysts selective to these reactions. The third boiler fuel requires that olefination/esterification be performed on the oxidized product by addition of alcohols and olefin. Both the esterification and olefination/esterification reactions are performed simultaneously with partial deoxygenation in the presence of pressurized syngas or pressurized hydrogen as previously described.
The production of the hyper-acidified product also allows for the production of three more boiler fuel types. These boiler fuels may, as described for the previous three fuel production embodiments, be converted to transportation fuel if full deoxygenation and blending to accepted petroleum fuel standards are achieved. The three boiler fuels produce by these methods may be utilized for heating or may be fully deoxygenated to hydrocarbon mixtures utilizing hydrogen or hydrogen with a percentage of CO added. The hydrocarbons are then distilled to their gasoline, aviation fuel or diesel petroleum equivalents followed by blending to a standard transportation fuel.
The syngas utilized for embodiments of the present invention may be produced by gasifying any material by any gasification method known in the art. The relative proportions of the gas types comprising the syngas may be in any proportion. For example coal syngas contains approximately 14.0% hydrogen, 27.0% carbon monoxide, 4.5% carbon dioxide, 0.6% oxygen, 3.0% methane, and 50.9% nitrogen. Syngas produced from biomass, by contrast, contains approximately 10.8% hydrogen, 24.0% carbon monoxide, 6.0% carbon dioxide, 0.4% oxygen, 3.0% methane and 48.6% nitrogen. The presence of nitrogen is not required as nitrogen transferred to the fuel product is no beneficial. Other gases, such as methane may be beneficial but is not important. Oxygen is not required. In certain embodiments, it is required, however, that a percentage of hydrogen be present in the syngas to deoxygenate the oxidized or hyper-acidified product. In addition, the production of additional hydrogen to allow syngas to produce hydrogen in situ requires the presence of a percentage of carbon monoxide to promote the water gas shift (WGS) reaction. The proportion of the hydrogen and carbon monoxide relative to each other may be in any ratio that is capable of performing the deoxygenation reaction. Alternatively, a synthetic syngas may be produced containing any proportion of the relevant percentages of hydrogen and carbon monoxide. As for syngas produced from coal or biomass other gases may be present if the deoxygenation reaction and WGS reactions are either improved or not blocked by their presence. When utilized, a second gas port on the hydrotreater may add a percentage of hydrogen or carbon monoxide if one of these gases is insufficient to perform the deoxygenation or WGS reaction. Other gases or mixed gases may be administered with either of these gases as long as they either improve or do not interfere with the deoxygenation or WGS reactions.
Production of drop-in fuels requires full deoxygenation step at a higher temperature than for the mild deoxygenation. The first-stage product from any one of the above described boiler fuels may be upgraded to a transportation fuel grade via full deoxygenation step with an appropriate full deoxygenating catalyst.
The fully deoxygenated product will produce a hydrocarbon mixture that must be distilled to component fuels equivalent to petroleum fuels (gasoline, aviation fuel and diesel) using the appropriate vapor distillation temperatures for the petroleum fuels. It is intended that these fuels will not be exact equivalents of the petroleum fuels but will be blended with petroleum fuels to meet the ASTM standard for each of the fuel types.
Additional procedures have been developed to process bio-oil. For example, one method to prevent bio-oil from polymerizing during what may be termed “mild hydrotreating” consists of utilizing a mild temperature regime in the range of 250 to 300° C. in the presence of hydrogen and a hydrotreating catalyst. Another similar process calls for a two-stage deoxygenation of bio-oil comprising a partial hydrodeoxygenation utilizing pressurized hydrogen followed by a full hydrocracking deoxygenation. In yet another known procedure, a hydrocracking of the bio-oil step follows a mild hydrotreating step in which low temperature is applied to accomplish partial hydrodeoxygenation. The hydrotreating step is performed on raw bio-oil in the presence of pressurized hydrogen. However, such procedures do not include catalytic deoxygenation of oxidized and/or hyper-acidified products from bio-oil oxidation and/or acid anhydride pretreatments, nor utilization of syngas to perform catalytic deoxygenation. Such procedures may produce products with limited yield and limited energy density.
Another known procedure may produce an alcoholysis product by reaction of one or more alcohols in a reactor at a temperature between 150 to 500° C. at pressures between 500 to 4000 psi. Following the alcoholysis step, the product may be hydrotreated at a temperature between 120 and 450° C. at pressures between 500 and 3500 psi. A high boiling point hydrocarbon solvent may be added following the alcoholysis step. Any excess hydrocarbon solvent is reclaimed and recycled as a portion of the high boiling point hydrocarbon solvent. However, such procedure does not include oxidized and acid anhydride acidification processes prior to their alcoholysis treatment. The known procedure also calls for hydrotreating following addition high boiling hydrocarbon solvents, and not esterification of the hyper-acidified product. Such procedures also may produce products with limited yield and limited energy density.
Another known procedure is configured to reduce coking during bio-oil hydrocracking. This procedure includes addition of a high boiling hydrocarbon derived from mineral crude oil. The petroleum derived mineral product must be added to the hydrodeoxygenated pyrolysis oil, produced with hydrogen under pressure, such that the oxygen content of the upgraded bio-oil is below 30%. Yet another known procedure includes adding high boiling hydrocarbon solvents to bio-oil upgrading steps to reduce coking during hydrotreating. The hydrocarbon solvent was added following an alcoholysis step catalyzed by application of hydrotreating. In such procedures, no hydrocracking is performed, and, accordingly, each procedure adds a high boiling point hydrocarbon to hydrotreated pyrolysis oil that has had oxygen removed by application of the hydrotreatment with hydrogen under pressure in the presence of a hydrotreating catalyst. In addition, such procedures do not include oxidized and acid anhydrideprocesses prior to hydrotreating step nor did they utilize syngas under pressure to achieve oxygen reduction via catalytic deoxygenation. In one case, the procedures also disclose hydrotreating prior to the addition of high boiling hydrocarbon solvents in order to insure low oxygen content, but do not disclose adding high boiling hydrocarbon both before and after a syngas catalytic deoxygenation step. Clearly, such procedures may produce products with limited yield and limited energy density.
An additional known procedure to produce diesel range hydrocarbons includes a starting material of a mixture of bio-oil C12-C16 fatty acids, C12-C16 fatty acid esters and C12-C16 triglycerides. The fat products can be obtained from plant oils and fats, animal fats and oils fish fats or oils fats obtained from gene manipulated plants, recycled fats of the food industry or mixtures of any or the above named fat sources. Raw untreated bio-oils are not a rich source of esters. This procedure does not disclose the production of oxidized and hyper-acidified products by oxidation and acid anhydride treatments of raw bio-oils prior to combining them with fats.
Clearly, there is a demand for a conversion method that is more cost effective, increases fuel yield, and produces more fungible fuels than currently available methods and compositions. The present invention satisfies this demand.